A control arrangement for a timepiece, whether such be for the winding thereof or simply for time setting, frequently employs a crown adapted to take up at least two axial positions and also capable of being driven manually in rotation. If the interior of the timepiece must be sealed from the external environment which includes dust and water, special measures must be undertaken in order to assure sealing of such crown in whatever positions it may occupy, as well as during its rotation.
FIG. 1 shows a known solution to the problem, such construction having been long employed by the assignee of the present application. In this drawing, a tube or pendant 4 is driven into a caseband 5. The crown cooperating with this tube includes a head 1 integrally formed with a central cylindrical portion 9 intended to receive a stem (not shown) in the threaded hole 7 and with a skirt 8. The interior wall of such skirt includes a first annular housing 2 of diameter slightly greater than the outer diameter of the tube and a second annular housing 3 of much greater diameter intended to receive a packing 40. The lower part of the second housing 3 is blocked by a ring 6 which may be set or driven and which has as function to maintain the packing 40 in place when the crown is axially displaced along the tube.
The construction of FIG. 1 shows at least two important disadvantages. The first difficulty in this construction is the necessity of having to change the entire crown during repairs which would normally necessitate only changing the packing since, in view of the presence of ring 6, the replacement of the packing alone is almost impossible. If such crown is of gold as is often the case, it will be understood that to discard it constitutes a substantial loss. The second difficulty exhibited by the construction as shown in FIG. 1 resides in the relative complexity for the manufacture of the crown and of the internal wall of its skirt which shows two different diameters 2 and 3, this necessitating calling on specialized manufacturers.
Attempts have already been made to overcome the difficulties cited hereinabove. Patent document CH-A-610 467 shows in effect a figure where the skirt of the crown exhibits an internal wall the diameter of which is constant over its entire height, this enabling simplification of the manufacture of the crown, and where a packing is placed in a housing provided in the tube, this enabling a relatively easy changing of said packing. However, the construction in this document exhibits a difficulty due to the fact that the skirt may become soiled and thus cause premature wear to the packing. Effectively, in view of the interstice separating the skirt from the tube, undesirable matter (dust, dirt, liquids) may soil the entire portion of the skirt located below the packing so that when the crown returns to its rest position, the seal comes into contact with such undesirable matter deposited on the skirt. Since such matters are often abrasive, the packing is damaged in scraping the skirt and quite rapidly loses its prime function which is to assure sealing of the crown.